The Stovebolt Site Forums The Shop Area Driveline Question about transmission

I have a 1954 chevy 5 window, half ton with a 1970 El Camino 250 ci engine. The codes on the tranny are I 21 5 or L 21 5, hard to tell. It is a 4 bolt 3 speed. The casting number is GM 12 380210. Is this a 55-68 Muncie? Thanks.

Cast iron or aluminum case?

Cast iron, do you know what it is? Thanks, Frank.

Your date code points to 1965. I can't find anything on the casting number. Check the casting number and post a couple photos. You may have either a muncie or a Borg-Warner T16.

Possibly a Saginaw car transmission made on Sep 21 1965. Photos would definitely be helpful as would any other casting numbers. Side covers, bearing covers, some model tailshafts all have casting numbers. Almost all Chevrolet casting numbers start with a 3. The casting number you gave isn't crossing over in any reference material I have.

See if there's a side cover casting number.

nikon photoshare here are a few pictures. The other casting numbers are: Side cover 3686832, tailshaft 3820223 or 8, GM 14K235. Thanks, Frank.

Hy fmartinmn, that is the standard three speed from a 55B - 59 Chevy truck, or 55 - 57 Chev car, non syncro first gear, I believe it's called an SM318, hope that helps.

Do you know if that is a Muncie or a Saginaw? Thanks, Frank.

Hy fmartinmn, I believe it is a Muncie, but I'm not positive.

I was unable to open the photos but if it has a 4 bolt side cover and the case measures about 22" overall it is likely a 55-57 car or a 55-61 truck. If it has the short tail shaft, about 15" overall, it could be a 58-64 car or a 62-67 truck. They have the same internal parts the main difference is the tail housing. The supplier I buy my transmission parts from calls it a Muncie. Others may disagree.
Fred

Thanks for the info, that was the way I was leaning.

Thanks for the info, I appreciate it. Frank.

It is indeed an SM318, specifically, it's froma '55 Chevrolet or GMc truck. The levers and side cover are the givaway. The levers going in opposite directions were '55 only, '56 they went to both levers pointing down like the Passenger version. The shift shafts and side cover are also unique to this application. The entie side cover assembly will directly interchange with the Passenger and later Truck version.
Saginaw or Muncie? According to a GM transmission specialist I spoke with, it's both and neither. The SM318 was made at both plants. The "Saginaw" and "Muncie" designations came much later, when GM got into manufacturing their own 4 speed Passenger transmissions, as well as each plant having their own version of the 7 bolt side cover 3 speed.

Thanks longbox55, I notice you have a overdrive tranny in your truck. I also have one that I plan to install in my truck. Is it worth the effort if I don,t change the rear end? Thanks, Frank.

Yes, it was well worth the effort (whis is minimal) to swap the overdrive in. I can cruise highway speeds and keep the rpm around 2000-2600 (55-75 mph).

Thanks again Bill.